The present invention relates to apparatus and methods for storing, detecting, and synchronously detecting servo information stored on disk drive media, and in particular to apparatus and methods useful within partial response, maximum likelihood detection channels and magnetic disk media.
By reading servo information recorded within data tracks on a disk surface, a disk drive head positioner servo system is able to estimate data transducer head position. The recorded servo information typically includes track (i.e. cylinder and head) addresses and servo bursts. Each circumferential data track on a disk surface has a unique track address, which is recorded in servo sectors embedded in the track, and servo burst patterns frequently repeat every two or more tracks. When a disk drive is seeking to a radial track location, the track addresses are used as coarse positioning information to approximately estimate the position of the read head and the servo bursts are used as fine positioning information to position the head precisely on the desired radial location.
At seek time while reading track addresses, the head may be positioned between two adjacent tracks. In this situation, the head may receive a superposition of signals from both tracks. One solution to this ambiguity is to encode the track addresses into Gray-coded addresses so that the encoded addresses of any two adjacent tracks differ from each other by only in a single bit position. With this solution, when the head is reading between two tracks, the ambiguity after decoding the address is one track, and an error of one track can be resolved during seek settle time, by reference to the servo burst or fine-position pattern.
In accordance with one known technique, each data track is divided into plural sectors. Each sector includes a header section, followed by a data section. The header section may typically include a DC erase field, a preamble field, a header synchronization character, a track address field (coarse servo information) and a servo burst field (fine servo information). The data section may typically include another preamble field, a data synchronization character, a block of user data, and error correction bytes. In this example, the header section is recorded at the same data rate as the data section, and synchronous peak detection through a single read channel structure in the disk drive is employed to read the information in both the header section and the data section. An example of this approach is found in commonly assigned U.S. Pat. No. 5,036,408 to Leis et al., entitled: xe2x80x9cHigh Efficiency Disk Format and Synchronization Systemxe2x80x9d, the disclosure thereof being incorporated herein by reference.
Another known technique is to employ radial zones or bands of concentric data tracks, each zone having a data transfer rate associated with disk radius of the zone. In this example, data areas are separated by a series of radially extending embedded servo sectors which are factory recorded with servo information at a single data transfer rate. A servo data recovery circuit asynchronously (i.e. without phase lock to incoming servo data) recovers a servo address mark, a track number and fine position information from information read by the data transducer while passing over each sector. The servo recovery circuit is separate from the read channel electronics employed for peak detection of user data information. This example is described in commonly assigned U.S. Pat. No. 5,420,730 to Moon, et al., entitled: xe2x80x9cServo Data Recovery Circuit for Disk Drive Having Digital Embedded Sector Servoxe2x80x9d, the disclosure thereof being incorporated herein by reference.
One factor which has limited data storage densities in magnetic recording employing peak detection techniques has been intersymbol interference, arising when flux transitions are increasingly close to each other. One technique for increasing flux densities in magnetic recording while still accurately reading recorded data is to employ synchronous sampling data detection. This technique, frequently referred to as xe2x80x9cpartial response, maximum likelihoodxe2x80x9d (PRML) signaling, has provided some improved data storage densities, at the expense of increased circuit complexity, including a fast analog to digital conversion process, and channel equalization, either on the analog side or on the digital side of the signal stream, or both. An example of a disk drive employing PRML is given in commonly assigned U.S. Pat. No. 5,345,342, to Abbott et al., entitled: xe2x80x9cDisk Drive Using PRML Synchronous Sampling Data Detection and Asynchronous Detection of Sector Servoxe2x80x9d, the disclosure thereof being incorporated herein by reference. The approach described in this patent enabled special circuitry within the synchronous sampling data detection channel to asynchronously detect track number values in embedded servo sectors recorded at a constant servo data rate whereas the user data rate differed by radial data zone across the recording disk. The servo bursts were read and processed using conventional peak detection, and sample and hold techniques.
An improvement over the asynchronous servo sampling technique taught by the Abbott et al. patent referred to above is found in a later, commonly assigned U.S. Pat. No. 5,384,671 to Fisher, entitled: xe2x80x9cPRML Sampled Data Channel Synchronous Servo Detectorxe2x80x9d, the disclosure thereof being incorporated herein by reference. In this approach a timing loop of the synchronous sampling data detection system is phase locked to servo information, the servo information including track address and fine position information is synchronously sampled and decoded. In this approach the servo preamble field is recorded as a conventional xc2xcT sine wave pattern, which corresponds to a 2T pattern in a peak detection channel (T representing a unit sample cell or interval).
While these prior approaches have worked well in their respective times, increasing data storage capacities and data transfer rates per unit size disk have led directly to a hitherto unsolved need for an improved disk drive head servo format and synchronous sampling servo detection method and architecture.
A general object of the present invention is to provide improved and simplified methods, apparatus, and data format for providing information for positioning data transducer heads relative to data tracks in a disk drive including a partial response, maximum likelihood (PRML) synchronous sampling data detection channel.
Another object of the present invention is to provide a servo format and apparatus for a PRML disk drive which does not require separate peak-detection hardware for detecting embedded servo information.
Yet another object of the present invention is to reduce impact of radial incoherence upon a head position servo system of a disk drive thereby facilitating higher track densities in a manner overcoming limitations and drawbacks of the prior art.
A further object of the present invention is to provide a synchronous sampling servo information estimation method and apparatus which makes substantial use of circuit elements of a PRML synchronous sampling data detection channel, thereby reducing overall circuit complexity and cost while providing for robust recovery of the servo information.
A further object of the present invention is to provide a simplified address decoding method and apparatus within a PRML sampling data detection disk drive.
One more object of the present invention is to provide a more compact and higher efficiency servo address format enabling use of higher code rates, smaller cell times and less redundancy within embedded servo sectors which are synchronously sampled and detected within a PRML disk drive.
Yet another object of the present invention is to employ a species of bi-phase self-clocking code, known as xe2x80x9cwide bi-phase codexe2x80x9d for encoding head position servo information recorded within embedded servo sectors on a storage disk surface of a disk drive including a PRML synchronous sampling data detection channel, in a manner facilitating use of many channel elements during servo information recovery operations.
Still one more object of the present invention is to provide a most-significant-bit (MSB) detector for detecting wide bi-phase encoded head position servo information within a PRML synchronous sampling data detection channel of a hard disk drive.
Yet one more object of the present invention is to provide a plurality of servo burst detection architectures for detecting antipodal and frequency modulated servo burst patterns in order to produce head position error signals within a hard disk drive including a synchronous sampling data detection channel.
In accordance with principles of the present invention, a magnetic disk drive has at least one rotating magnetic data storage disk defining recording tracks divided into data sectors by narrow servo spokes. A data sector lying between servo spokes of a recording track on the disk is recorded with user data encoded in accordance with a code having a predetermined distance and user data code rate. Each servo spoke of the recording area has at least one servo information field encoded in a wide bi-phase pattern at a servo code rate which is selected to be reliably robust in view of the synchronously detected data code rate. The disk drive further includes a synchronous sampling data detection channel for synchronously sampling and detecting both the servo information field and the coded user data. The detection channel includes:
a data transducer head positioned by a servo-controlled head positioner over the recording track,
a preamplifier for receiving electrical analog signals magnetically induced by the data transducer head from flux transitions present in at least the servo information field,
a digital sampler for synchronously sampling the electrical analog signals to produce digital samples, and
wide bi-phase decoding circuitry including a most significant bit detector coupled to receive digital samples from the synchronous sampling data detection channel for decoding the coded wide bi-phase pattern.
In one aspect of the present invention, the data detection channel includes a chunk synchronizer for generating and applying a wide bi-phase synchronization signal to the most significant bit detector.
In another aspect of the present invention, the wide bi-phase magnet patterns recorded in plural servo information fields of each spoke are ++xe2x88x92xe2x88x92 for a binary zero information value and xe2x88x92xe2x88x92++ for a binary one information value.
In another aspect of the present invention, one servo information field within each spoke comprises a track number binary pattern of predetermined bit length, the pattern being decoded as a wide bi-phase code and then decoded as a Gray code with a code rate of one. Also, the track number binary pattern may include a parity or cyclic redundancy check (CRC) symbol, and has circuitry for receiving and decoding the track number binary pattern and for checking the parity or CRC symbol.
In a further aspect of the present invention, one servo information field within each spoke comprises two track number binary patterns of predetermined bit length: a first track number being an address of the track, and a second track number being an address of a second track adjacent the track. In this aspect, the second track number may be recorded with a one-half track offset extending into the second track, and it may further include error correction code values calculated with respect to the first and second track numbers. In this aspect, error correction code decoding and correcting circuitry is coupled to the synchronous sampling data detection channel for decoding, checking and correcting the decoded values of the first and second track numbers.
As another facet of the present invention, a data recording disk has a pattern of radially spaced tracks and a plurality of circumferentially spaced angular servo sectors lying in data sectors. The servo sectors include prerecorded servo head positioning information for identifying track and sector locations, each of the servo sectors having at least one identification field including servo symbols encoded in accordance with a wide bi-phase code. Each of the data sectors is recorded with data symbols in accordance with a maximum distance code such that the servo symbols and the data symbols may be detected by passage through a single synchronous sampling data detection channel, such as a PRML channel, with which the disk is physically assembled and used.
These and other objects, advantages, aspects and features of the present invention will be more fully understood and appreciated upon consideration of the following detailed description of a preferred embodiment, presented in conjunction with the accompanying drawings.